Add footer preference into caption preferences

Add footer preference into caption preferences to tell users
that the setting doesn't support all apps.

Reference link of screenshot:
https://drive.google.com/file/d/1VzpWa4M-4HjlfjDNNqrEIKwo3v0y_f51/view?usp=sharing

Bug: 135888603
Test: Visual
Change-Id: I95e0aa301eba7343fbc798cc406c0242f4f4eb7e
Merged-In: I95e0aa301eba7343fbc798cc406c0242f4f4eb7e
(cherry picked from commit 8f4b8b9a)